Why would you play dutch in the first place?

The greatest game of chess ever played was a Dutch Defense.

Bogoljubov vs Alekhine, Hastings 1922.

Black sacrificed his Queen and both Rooks, then advanced a Pawn and Queened it, sacrificed his SECOND Queen, advanced another Pawn and Queened it, sacrificed his THIRD Queen, and was advancing another Pawn to promote into yet another Queen when Bogoljubov resigned.

2...g6 is most popular, and playable. everyone know that black couldn't trap that bishop so there is no points for h6 -> g5 push

Putting double !! on Bg5 is a joke... it's not a special move by any means.

Even if it's not a special move, it's the best solution to avoid a bunch of main line theory in Leningrad Dutch.

That moment when the book you have is outdated by almost 20 years

Class players need not worry whether GMs regard the Dutch as highly as the Nimzo-Indian. It's an adequate QP defense and all players need a QP defense.

I'm surprised no one has mentioned the biggest sell for the Dutch to class players. Once White plays 1.d4 and Black plays 1...f5, the game is Dutch and Black will almost certainly have a strong opening knowledge advantage, since White QP players don't see the Dutch nearly as often as the other QP defenses.

Furthermore, the Dutch is not as theory-heavy as other QP defenses. Dutch strategies aren't that hard to grasp. Plus it can lead to lively games, as many enjoy.

The Dutch is a good answer for class players who have limited time for opening study but still like to be more booked than their opponent. It also synergizes with the French, if that is Black's KP defense.

Both 2...g6 and 2...h6 are good. Actually I think that 2...h6 is the more dynamic choice.

Honestly the Hopton attack is hard to play against, as it's counter-intuitive to the Dutch style; at least, that's my experience. So instead, I just avoid all the hassle with 1...e6 like others have mentioned in here. 

2... h6 must be playable but there is such a maze of variations after 3. Bh4 g5 4. e4 it becomes impractical for everyday chess. 4. e4 Rh7!? 5. Qh5+ Rf7 6. Nf3 Nf6 7. Qg6 Nc6 of Black Dog video fame and now White has many moves but I couldn't find one leading to a clear advantage, and 4. e4 Nf6 5. e5 e6 6. Bg3 f4 7. Bd3 d5 were ok for Black last time I checked but this is insanely complicated to maintain these lines in a repertoire for an amateur. The more reasonable 4. e3 must be +/= but as they say, obviously not terrifying, so suitable for both colors.

And as to why to play the Dutch? Because it's heaps of fun! Who doesn't love to attempt to blow their opponents off the board with the black pieces?

I love it not only for the double-edged, risky style of play that it often brings, but also because when you play the Dutch, you tend to know the theory better than your opponent (unless your opponent is an opening wizard, in which case, it's a good learning experience), as most players of 1. d4, 1. c4, 1. Nf3 etc. do not prepare for the opening as much as you do! 

I recall Stiepan (I think that's how you say his name), the man who runs the Hanging Pawns YouTube channel, suggesting that whilst 2... h6 and g6 are both playable, he'd much prefer to play 2...g6 to avoid all of the complications. 

Kasparov played 2.Bg5 against a 2600 GM, and Kasparov was unable to find a win.

You would think, if 2.Bg5 was that powerful, then one of the greatest players of all time should be able to easily dominate a mid-level GM with it. But the Dutch held.

And I'm guessing, with "best" play, the Dutch likely holds against everything.

They do test games in the Top Chess Engine Championships, and occasionally they do engine matchups with limited opening books (where only move 1 is book, and every move after that is pure engine).

In the 1.d4 f5 games, the Dutch is usually a draw. Even at the top level, with titans like Leela at the wheel, black is still able to hold.

So I'm not convinced that there even exists a way to beat it. At best, white can put pressure on it, and hope that black makes a false step along the way ... (Though I suppose that could be said about most defenses.)

I heard the grob/grog cant be defeated either so at least they have that in common.

I dont know about bongcloud.

2...h6 actually does the same, as ...g5 and ...Bg7 will follow. You just do not have to bother about "subtleties" like castling.

Ah, that dogmatism.

What about 4.e4 Bg7?

5.Bg3 is forced, and now Black even has a choice between 5...d6, 5...fxe4 and 5...Nc6!?

4.e3 or 4.Bg3 are better moves, but Black will play 4...Bg7! again. The check at h5 is not harmful at all- the king willl go to f8 and Black will have a few tempos handy while hitting at white's center.

There is nothing wrong with 2...g6, but 2...h6 is the most "Dutch" approach.

I have stopped playing 2.Bg5 because I have found nothing resembling an advantage against it.